One example of a prior art technique for enabling efficient use of disk space in a storage subsystem is the art of thin provisioning. According to thin provisioning, triggered by the generation of a write I/O (Input/Output) access to the virtual volume, a real volume space (space within a physical media) is dynamically allocated. Usually, the space of the volume to be allocated is divided into units of pages (each of which corresponds to a few hundred tracks), and the management information thereof is stored in a shared memory of the storage subsystem. Patent literature 1 discloses an art related to thin provisioning.
According to U.S. Pat. No. 7,613,896 (Yamamoto et al.), real storage areas to virtual storage areas, the allocation of real storage areas to virtual storage areas and the address conversion from the virtual storage areas to the real storage areas are performed, triggered by a host write access to the virtual storage area. The amount of management information related to address conversion required for input and output of data to or from the virtual storage area is increased in proportion to the number of virtual volumes or the capacity thereof, but this problem is solved by storing the management information in storage devices such as HDDs (Hard Disk Drives) which have low access performance compared to shared memories but are inexpensive.
Further, if the unit of volume space to be allocated is managed in page units (approximately a few hundred tracks) and in track units, the allocation of volume space in track units requires management information in track units to be stored in addition to the management information in page units. The management information in track units is also stored in the storage devices. The management information in track units is stored in a TSE (Track Space Efficient) volume which is a volume accessible via cashing control among a cache memory and storage devices. The TSE volume is divided into a TSE DMT (Dynamic Mapping Table) section storing the management information table in track units and a user data section storing the actual user data, which are composed of separate pages. It is indispensable to refer to the TSE DMT when accessing the TSE volume.